Method of combustion and a combustion plant in which absorbent is regenerated

Abstract

A method of combustion and a combustion plant in which absorbent is regenerated is described herein. During the combustion of a fuel in a combustion chamber enclosing a fluidized bed, a fuel and an absorbent are supplied to the fluidized bed. The combustion gases generated during the combustion are collected and purified in a separating member by separation of solid material from the combustion gases. The separated solid material is recirculated to the fluidized bed through a channel, and a gaseous medium is supplied in a controlled manner to the separated solid material present in the channel in order to displace the combustion gases and provide a chemical reaction.

What is claimed is:  
     
       1. A method of combustion of a fuel, comprising the steps of: 
       combusting the fuel in a combustion chamber enclosing a pressurized fluidized bubbling bed to form combustion gases in the combustion chamber;  
       supplying an oxygen-containing gas to the bed from beneath;  
       supplying a lime-containing absorbent to the bed;  
       collecting combustion gases formed during the combusting step;  
       purifying the combustion gases by separating solid material therefrom; and  
       recirculating the separated solid material to the combustion chamber through a channel, wherein the channel has an orifice connected to the bed, and a gaseous medium is supplied in a controlled manner to the separated solid material present in the channel to displace the combustion gases therein so that the partial pressure of carbon dioxide in the channel is lowered, thereby permitting a reaction of the absorbent in the channel to quick lime.  
     
     
       2. A method according to  claim 1 , wherein the combustion chamber comprises a space above the bed, and the channel is located in the space and in the bed. 
     
     
       3. A method according to  claim 1 , wherein the gaseous medium is preheated prior to being supplied to the separated material in the channel. 
     
     
       4. A method according to  claim 3 , wherein the gaseous medium is preheated to a temperature of about 600° C. to 900° C. 
     
     
       5. A method according to  claim 1 , wherein the gaseous medium comprises air. 
     
     
       6. A method according to  claim 1 , wherein the gaseous medium comprises steam. 
     
     
       7. A method according to  claim 1 , wherein the gaseous medium comprises nitrogen. 
     
     
       8. A method according to  claim 1 , wherein the gaseous medium comprises a combination of at least two gases selected from the group consisting of air, nitrogen, and steam. 
     
     
       9. A method according to  claim 1 , wherein the gaseous medium is supplied to the channel at a plurality of levels. 
     
     
       10. A method according to  claim 9 , wherein air and/or nitrogen are/is supplied to the channel at a higher level and steam is supplied to the channel at a lower level. 
     
     
       11. A method according to  claim 1 , wherein the length of time the material resides in the channel is increased by an enlarged portion of the channel. 
     
     
       12. A method according to  claim 1 , wherein the absorbent comprises limestone or dolomite. 
     
     
       13. A method according to  claim 1 , wherein the material is supplied to the channel in such a manner that the weight of a column of material recirculates the material in a continuous flow through a passage having a constant opening area and being provided in a lower portion of the channel. 
     
     
       14. A method according to  claim 13 , wherein the height of the column of material exceeds the height of the bed. 
     
     
       15. A method according to  claim 13 , wherein the oxygen-containing gas provided to the bed from beneath is prevented from entering the channel. 
     
     
       16. A combustion plant comprising: 
       a combustion chamber enclosing a pressurized fluidized bubbling bed, wherein a fuel is combusted and forms combustion gases within said combustion chamber while a lime-containing absorbent is supplied to the bed;  
       a purification device for purifying the combustion gases, said purification device having a separating member for separating particulate material from the combustion gases, and a channel connecting the separating member and said combustion chamber for recirculating the separated material to said combustion chamber, wherein the channel has an orifice connected to the bed;  
       at least one gas supply member connected to the channel for supplying a gaseous medium to the separated material present in the channel to displace the combustion gases in the channel, lower the partial pressure of carbon dioxide, and enable reaction of the absorbent; and  
       a heat exchanger provided in said combustion chamber for preheating the gaseous medium supplied to said at least one gas supply member.  
     
     
       17. A combustion plant according to  claim 16 , wherein said combustion chamber comprises a space above the bed, the channel being located in the space and in the bed. 
     
     
       18. A combustion plant according to  claim 16 , wherein said at least one gas supply member supplies air to the material present in the channel. 
     
     
       19. A combustion plant according to  claim 16 , wherein said at least one gas supply member comprises at least one gas feeding device provided in a wall of the channel. 
     
     
       20. A combustion plant according to  claim 19 , wherein the at least one gas feeding device comprises a cylinder provided around the channel and having a limiting wall so that a closed annular space is formed between the channel and the cylinder, and the wall of the channel comprises a passage between the interior of the channel and the closed annular space. 
     
     
       21. A combustion plant according to  claim 16 , wherein said at least one gas supply member comprises a plurality of gas feeding devices supplying the gaseous medium to the channel at a plurality of levels. 
     
     
       22. A combustion plant according to  claim 16 , wherein the channel comprises an enlarged portion that increases the volume of material held in the channel. 
     
     
       23. A combustion plant according to  claim 16 , wherein the channel comprises passive portions, and a column of material is formed in the channel during the operation of the combustion plant, the passive portions forming a passage in the lower part of the channel that permits the weight of the column of material to discharge the material therethrough in a continuous flow. 
     
     
       24. A combustion plant according to  claim 23 , wherein the passage has a constant flow area. 
     
     
       25. A combustion plant according to  claim 23 , wherein the column of material formed during the operation of the combustion plant has a height exceeding the height of the bed in said combustion chamber. 
     
     
       26. A combustion plant according to  claim 23 , wherein the passive portions prevent a gas from beneath from entering the channel. 
     
     
       27. A combustion plant according to  claim 23 , wherein the passive portions comprise surfaces provided at a lower end of the channel and covering a majority of the cross-sectional area of the channel. 
     
     
       28. A combustion plant according to  claim 27 , wherein the surfaces form an angle of inclination to a vertical axis of about 20° to 90°. 
     
     
       29. A combustion plant according to  claim 16 , wherein said combustion chamber and the separating member are enclosed in a pressure vessel, the combustion plant further comprising compressors maintaining a pressure above atmospheric pressure in the pressure vessel. 
     
     
       30. A combustion plant according to  claim 16 , wherein the bed has a height between about two meters and six meters. 
     
     
       31. A combustion plant according to  claim 16 , wherein the channel orifice connects to the bed beneath a tube arrangement provided in the bed for heating water and/or superheating steam. 
     
     
       32. A combustion plant according to  claim 16 , further comprising compressors for feeding oxygen-containing gas at a velocity of 0.5 m/s to 2.0 m/s to the bed through nozzles provided beneath the bed.